The sensed signals are, for example, waves propagated from a seismic source disposed on the surface or in another well and have been reflected by the discontinuities of the subsurface.
The acquisition of measuring data in a drilling is generally effected by lowering into the drilling a number of sensors connected to a single probe or a set of several probes suspended from a multifunctional cable. The probe or each probe comprises an elongated body and anchorage means enabling it to be coupled with the walls of the well. The sensors may be disposed in skids brought into contact with the walls by activating the anchorage means. They may also be disposed in the body of the probe and the anchorage means are disposed in such a way so as to laterally move the body and bringing the sensors into contact with the walls. The anchorage means comprise, for example, jacks fed with compressed fluid by a hydraulic system inside the body and the probe or even by springs whose release is provoked by unlocking a bolt.
The multifunction cable usually comprises a plurality of conductive lines allowing for the transmission of electric currents in order to feed the motor and all types of signals. This involves, for example, control signals transmitted to the probe from a surface laboratory and response signals sent from the sensor. The response signals are constituted by either control or test signals or by data measured by the sensors of the probe.
Various probes are, for example, described in the French Patents 2.501.380, 2.548.727 or 2.564.599 or the U.S. Pat. No. 4,578,785.
The embodiment of extended seismic sections able to be easily exploitable requires the use of receiving devices able to detect seismic signals at a large number of points at different depth levels. The receiving device must be able to be quickly moved along the wall. At each anchorage location, the coupling of sensors with the walls must be as effective as possible so as to capture the seismic signals and not unwanted signals propagating in the water column generally filling the well. The anchorage device to be used is becoming more and more complex and difficult to implement.